The present invention relates to turbomachines such as those used in the field of aeronautical engineering. It relates to the variable-pitch stator vanes of turbomachines, particularly of gas turbine engine compressors, and more especially to the control levers that rotate such vanes about their pivot.
Gas turbine engines comprise an air-compressor-forming section feeding a combustion chamber which produces hot gases which, downstream, drive the turbine stages. The engine compressor comprises a plurality of moving bladed disks or blisks, separated by successive stages of stator blisks that straighten the gaseous flow. The vanes of the first flow straightener stages are generally variable-pitch vanes, that is to say that the angular position of the vane about its radial axis, that acts as a pivot, can be adjusted according to mission points in order to improve compressor efficiency. The variable-pitch vanes are oriented using a mechanism known as a variable-pitch mechanism or a VSV which stands for variable stator vane. There are various designs of such mechanisms, but on the whole, they all comprise one or more actuators fixed to the engine casing, synchronization bars or a control shaft, rings surrounding the engine and positioned transversely with respect to the axis thereof, and substantially axial levers also known as pitch control rods, connecting the rings to each of the variable-pitch vanes. The actuators rotate the rings about the engine axis and these cause all the levers to turn synchronously about the vane pivots.
These mechanisms are subjected both to the aerodynamic loads applied to the vanes, which are high, and to loads resulting from friction in the various connections. In particular, the levers are subjected to static loadings in bending and in torsion and to dynamic stresses. All of these loads may reach levels liable to be damaging; in particular, their combined effect may lead to the formation of cracks or to other damage. Given the mechanical strength and endurance requirements attributed to them, the amplitudes of any vibrations caused by these loads, and to which these components are subjected, need to remain small.
The components are designed and engineered in such a way as to avoid there being any critical modes in their operating range. However, in practice, there are still some overlaps and experience, during engine testing carried out at the end of the component design cycle, has revealed that, in some cases, that could lead to cracks being formed in the levers. The component has then to be re-engineered and modified, this being a particularly lengthy and expensive process. It is therefore necessary to predict the vibrational response levels as early on as possible in the component engineering cycle so that the necessary corrective measures can be taken as early on as possible in the design process.